Displays including thin film transistors have been widely spread and indispensable to our life. In addition, these displays are very important for portable displays and have been necessary for portable terminals.
Furthermore, display devices in which a display region (a pixel portion) and a peripheral circuit (a driver portion) are provided in the same substrate have been widely used. For example, Patent Document 1 discloses a technique of using oxide semiconductor transistors in the display region and the peripheral circuit. When the display region and the peripheral circuit are formed simultaneously, the manufacturing cost can be reduced.